The present invention relates to a method of winding a yarn into a cylindrical cross-wound package in a step precision wind.
When winding synthetic filament yarns to cross-wound packages, there arises the problem of a so-called "ribbon formation." As the diameter of a package increases, a ribbon always forms when one or more complete package revolutions occur per double stroke, i.e., when the ratio of the rotational package speed to the double stroke frequency of the yarn traversing mechanism is equal to 1, an integral multiple, or an integral fraction. A double stroke is defined as a complete forward and back movement of a traversing yarn guide. The ratio of rotational speed of the cross-wound package to the double stroke frequency of the traversing mechanism is generally designated as the winding ratio K. The ribbons, which are also named ribbon winds, lead to certain disturbances when unwinding the yarn. Furthermore, during the winding, ribbons lead to vibrations of the takeup machine and, thus, to an uneven contact of the contact pressure roll on the package, and finally also to damage of the package. It is therefore necessary to avoid ribbons in particular in the case of flat yarns, such as, for example, synthetic fibers.
The winding of yarns to cross-wound packages may occur in random wind, precision wind, or in a step precision wind. In the case of the random wind, the package is built up at a constant circumferential speed of the package and at a constant traversing frequency. This results in that the winding ratio K, which represents the ratio of winding spindle speed to double stroke rate of the traversing mechanism, decreases constantly in the course of a winding cycle. This is caused by the fact that the rotational speed of the winding spindle decreases likewise as the package diameter increases. In this process, ribbons are bound to form, when the winding ratio becomes an integer or assumes values which differ from the next whole-numbered wind ratio by a common fraction. A "common" fraction denotes a fraction, whose denominator is a whole number, such as, for example 1/2; 1/3; 1/4.
In a precision wind, the package is built up at a traversing speed, which is directly proportional to the rotational speed of the winding spindle. This means that in a precision wind, the winding ratio is a predetermined constant and remains constant in the course of the winding cycle, whereas the traverse frequency decreases proportionately to the winding spindle speed with the winding ratio being the factor of proportionality. In comparison with a package wound in random wind, a package wound in precision wind has certain advantages. In particular, a precision wind facilitates reduction of the ribbon formation by predetermining the winding ratio.
The so-called stepped precision wind or also step precision wind (SPW) differs from the precision wind only in that the winding ratio remains constant only during predetermined phases of the winding cycle. From phase to phase, the winding ratio is decreased in steps by a sudden increase of the traversing speed. This means that in the step precision wind, a precision wind occurs within each phase or step, during which the traversing speed decreases proportionately to the spindle speed. After each phase, the traversing speed is again suddenly increased, so as to result in a decreasing winding ratio. In so doing, the winding ratios, which are to be maintained during the individual phases are previously computed and programmed.
EP 0 578 966 B1 discloses a winding method, wherein a computer determines the winding ratio from step to step of a step precision wind and compares same with critical ribbon values. In this instance, one operates with computed winding ratios, when same are not within the critical range of a ribbon value. However, when a winding ratio is within the critical range, one will operate only with a slightly modified winding ratio. This means, that in the case of critical ribbon values one will operate with so-called (near-to-ribbon) winding ratios, which represent a winding ratio that differs from a ribbon value by a defined slight difference. Likewise disclosed is that the spacing of the yarn displacement is related to the distance between yarn centers. This displacement spacing is at least equal to the width and at most equal to three times the width of the overlying yarn. This means, that the yarn thickness is considered in the takeup operation.
EP 0 194 542 B1 discloses a method of winding yarn, in particular synthetic filament yarns in spin and draw machines. In this method the step precision wind is applied, and an inaccuracy of the winding ratio is deliberately generated. A modulation of the winding ratio is realized in a certain modulation width, in which the traversing speed changes by a small defined amount with respect to a computed and programmed value of the traversing speed.
Furthermore, EP 0 055 849 B1 discloses a method of winding yarns or tapes in a step precision wind, wherein the change of the winding ratio from one step of the precision wind to the next is made so small that the thereby caused changes in the takeup speed of the yarn or tape do not exceed 3%, preferably 0.3% of the average takeup speed.
Common to all known methods of the prior art is that they are unable to prevent primarily ribbon formations of a higher order or even honeycomb formations, i.e., to take also into account primarily rare ribbons, and that therefore even a step precision wind, as is known from the state of the art, is unable to prevent ribbon formations in general.
It is therefore the object of the invention to provide a method of winding yarns, which permits the reliable production of cylindrical cross-wound packages with satisfactory unwinding characteristics, i.e, substantially without ribbons of even a higher order and of a rarer kind and without honeycombs.